The present invention relates to a process for the hydroformylation of olefinically unsaturated compounds having 3 to 12 carbon atoms with hydrogen and carbon monoxide at increased pressure.
In the hydroformylation of olefins with carbon monoxide and hydrogen aldehydes and alcohols are produced with the aldehydes and alcohols having one carbon atom more than the starting olefin. The catalyst is herein conventionally used in homogeneous phase with the olefin. The reaction is preferably catalyzed by hydridrometal carbonyles of the metals of group VIII of the periodic table of elements. Apart from cobalt, which is used extensively as a catalyst metal in technical applications, rhodium has acquired increasing significance preferably for the hydroformylation of lower olefins. In contrast to cobalt, rhodium permits carrying out the reaction at low pressure, moreover, when using terminal olefins preferably straight-chain n-aldehydes are formed and only secondary iso-aldehydes. Furthermore, the hydrogenation of the olefinic compounds to form saturated hydrocarbons in the presence of rhodium catalysts is also markedly lower than is the case when using cobalt catalysts.
In methods introduced in technology the rhodium catalyst is used in the form of modified hydridorhodium carbonyles, which additionally and, if appropriate, comprise ligands in excess. Especially useful have been found to be ligands of tertiary phosphines or phosphites. Their application permits lowering the reaction pressure to values below 30 MPa.
For example, DE 27 43 630 relates to the production of alkane polyols (glycols) from synthesis gas using a crown ether comprising at least 4 oxygen atoms as solvent. This crown ether serves for separating ions from the homogeneous liquid phase without the simultaneous complex formation of the rhodium-containing catalyst. The reaction temperatures in all examples are above 220xc2x0 C.
In U.S. Pat. No. 4,320,064 is described the reaction of carbon monoxide with hydrogen to form polyols using rhodium carbonyl clusters in a homogeneous liquid phase. As the catalyst a cesium salt of [Rh22(CO)35Hx]nxe2x88x92 complexed by 18-crown-6 is used. Here also the crown ether serves for the complexing of the cationic component of the rhodium carbonyl cluster. The temperatures specified in the examples are between 250 and 270xc2x0 C.
However, in these methods the separation of the reaction products and the recovery of the catalysts homogeneously dissolved in the reaction product presents problems. In general, for this purpose, the conversion product is distilled out of the reaction mixture. Due to the thermal sensitivity of the formed aldehydes and alcohols, this approach can only be followed in practice in the hydroformylation of short-chain olefins with 3 to 5 carbon atoms.
In the hydroformylation of olefins with more than 6 carbon atoms, products with high boiling point are formed which cannot be separated by distillation from the homogeneously dissolved rhodium complex catalyst. Through the formation of heavy oil, the thermal loading of the distillation material leads to considerable losses of valuable products and of catalysts through the decomposition of the rhodium complex compounds.
The problem of thermal decomposition is avoided if a two-phase catalysis is used. Herein two liquid phases not miscible with one another are present of which the one organic phase contains the olefin and the other, most often polar phase, contains the catalyst. Prerequisite for the application of this process is the solubility of the catalyst in the polar phase. On an industrial scale as the polar phase is used an aqueous phase and as the catalyst a rhodium complex compound. The solubility of the catalyst in the aqueous phase is herein attained by using sulfonated triaryl phosphines as complex component. After completing the hydroformylation reaction, the separation of the catalyst from the reaction product in this process variant takes place simply by separation of the aqueous and organic phase, i.e. without distillation and thus without additional thermal process steps. Such a process is described for example in DE 26 27 354. A special characteristic of this mode of operation is that from terminal olefins with high selectivity are formed n-aldehydes and only to a minor degree iso-aldehydes (i.e. aldehydes branched in the xcex1 position to the aldehyde group). In addition to sulfonated triaryl phosphines, carboxylated triaryl phosphines are also used as complex components water-soluble rhodium complex compounds.
The use of a water-soluble catalyst has also been found to be useful in the hydroformylation of lower olefins, in particular propene and butene. However, if higher olefins such as pentene or hexene are used, the conversion rate is already markedly reduced. The economy of the conversion on an industrial scale is frequently no longer given to the desired extent when using olefins with more than four carbon atoms.
In order to increase in the hydroformylation of olefins with more than 5 carbon atoms by means of water-soluble catalysts the conversion and/or the selectivity of the reaction to n-aldehydes, special amphiphilic reagents or solubilizers have also been used.
The addition of these substances leads to the fact that the transport of matter between the discrete phases and thus the miscibility of the aqueous catalyst phases and organic phase are promoted.
DE 34 12 334, for example, relates to the hydroformylation of olefins using quaternary ammonium salts. As is evident in Table 4, the hydroformylation of hexene by means of rhodium and trisodium tris(m-sulfophenyl)phosphine without the addition of a solubilizer leads to a conversion of 36% (Example 10), while the addition of polyols as solubilizer (Example 11: 5% polyglycol 200; Example 14: 2.5% triethylene glycol) only brings about a conversion of 43.5% or 43%, respectively. A very high conversion, 86%, in contrast, is attained through the addition of 2.5% trimethyl hexadecyl ammonium bromide as solubilizer. This publication shows that only the addition of quaternary ammonium salts causes a considerable increase in the conversion. In contrast, neither the addition of tri- or polyglycols, not an increase of the quantity of these substances by the twofold (from 2.5 to 5%) causes a significant increase of the conversion.
In DE 31 35 127 A1 the hydroformylation of olefins is described using amphiphilic reagents in the presence of a rhodium catalyst complexed by a phosphine ligand. Table 7 shows that the hydroformylation of 1-dodecene by means of rhodium and monosulfonated triphenyl phosphine (3-Ph2PC6H4SO3Na) without the addition of an amphiphilic reagent leads to a conversion of 56% (Example 77), while the addition of 18-crown-6 leads to a decrease of the conversion to 40% (Example 57). In this case also high yields are only attained by using quaternary ammonium salts (Example 68: 85% with CTAB).
A substantial disadvantage in using quaternary ammonium salts as amphiphilic reagents lies, however, in their poor biological degradability. For example, the presence of quaternary ammonium salts in the waste water leads to considerable difficulties in waste water treatment.
A further disadvantage in using quaternary ammonium salts as solubilizers lies therein that the increase of the miscibility of the aqueous catalyst phase and the organic phase achieved with these compounds is accompanied by increased solubility of the organic phase in the aqueous phase and of the aqueous phase in organic phase. In this way, to an increasing degree amphiphilic reagent and solubilizer as well as also rhodium and water-soluble phosphines can be present in the organic phase and, after phase separation, can be discharged with the organic phase. It is understood that the discharge of these substances via the organic phase is undesirable since new substances must again be added to the same extent to the aqueous phase to the same extent, which, in particular in view of rhodium, entails considerable increased financial expenditures.
Furthermore, with a higher addition of amphiphilic reagents or solubilizerxe2x80x94i.e. with increased miscibility of the aqueous catalyst phase and the organic phasexe2x80x94the separation into components necessary for the phase separation no longer takes place or takes place to an insufficient extent due to the formation of emulsions or solutions. This is in particular the case with such amphiphilic reagents which can also be used as tensides or foaming agents.
This is of disadvantage since good separation into components is an indispensable prerequisite for the required separation, completing the hydroformylation, of organic and aqueous phase.
The task of the invention comprises providing a process for the production of aldehydes through the hydroformylation of olefins with 3 to 12 carbon atoms, which makes possible greater conversions in comparison to prior art and which avoids the disadvantages of prior art.
This task is solved through a process for the production of aldehydes through the conversion of an olefin with 3 to 12 carbon atoms with hydrogen and carbon monoxide in the presence of a rhodium catalyst, characterized in that
(a) the rhodium catalyst is present in an aqueous phase with the aqueous phase comprising
i) rhodium in elementary or bound form;
ii) a trisulfonated triaryl phosphine, and
iii) a crown ether, and
b) the olefin under the reaction conditions is present in a liquid organic phase which is not miscible with the aqueous phase.
The process according to the invention is in particular distinguished thereby that in comparison to prior art, higher conversions with high selectivity are attained and that no significant rise of rhodium or ligand in the organic phase and thus no increased discharge of the catalyst via the organic phase is observed.
Furthermore, the capacity for being separated of the organic phase and the aqueous catalyst phase is so high that a rapid separation of organic phase and aqueous phase is ensured. When applying this process neither emulsions difficult of separation nor nonseparatable homogeneous solutions are formed.
The crown ethers to be used according to the invention are described for example in xe2x80x9cUllmann""s Encyclopedia of Industrial Chemistryxe2x80x9d Weinheim (1987), Fifth Edition, Volume A8, pp. 91-97.
The trisulfonated triaryl phosphine is, according to a preferred embodiment a trisulfonated triaryl phosphine having the formula (I) 
in which
Ar1, Ar2 and Ar3 independently of one another represent a phenyl, naphthyl, biphenyl, phenylnaphthyl or binaphthyl group;
M1, M2 and M3 independently of one another represent an alkali metal ion or an ammonium ion.
But it is also possible that M1, M2 and M3 represent different higher cations such as, for example, alkaline earth or zinc ions, with the charge equalization determining decisively the number of these cations.
This trisulfonated triaryl phosphine having the formula (I) is especially preferably trisodium tris(m-sulfophenyl) phosphine having the formula 
Due to its production by sulfonation of triphenyl phosphine, this trisodium salt contains fractions of mono- and disulfonated compounds and small fractions of the corresponding phosphine oxides.
The trisulfonated triaryl phosphine can also be a sulfonated triaryl phosphine with two phosphorus atoms, which comprises, for example, a group xe2x80x94(CH2)xxe2x80x94Arxe2x80x94Arxe2x80x94(CH2)xxe2x80x94 in which
x represents an integer between 1 and 4, in particular 1 to 2, preferably 1,
Arxe2x80x94Ar is biphenyl or binaphthyl,
the group xe2x80x94(CH2)x with one bond is in the ortho position with respect to the aryl-aryl bond Arxe2x80x94Ar connecting the two aryl groups, and with the other bond is bound to one phosphorus atom which has two further, identical or different aryl groups, in particular phenyl groups.
Examples of such trisulfonated triaryl phosphines having two phosphorus atoms are compounds having the formula (II) 
in which
m1 and m2 can have the value 0 or 1, with the sum of m1 and m2 being at least 1, and
M1, M2, M3 and M4 independently of one another represent each an alkali metal ion or an ammonium ion.
But is also possible that M1, M2, M3 and M4 represent different, higher cations such as for example alkaline earth or zinc cations with the charge equalization decisively determining the number of these cations.
The organic trisulfonated triaryl phosphine can also be a compound having the formula (III) 
in which
m3, m4, m5 and m6 can have the value 0 or 1, with the sum of m3, m4, m5 and m6 being at least 2, and
M1, M2, M3, M4, M5 and M6 independently of one another represent each an alkali metal ion or an ammonium ion.
In this case it is also possible that M1, M2, M3, M4, M5 and M6 represent different, higher cations, such as for example alkaline earth or zinc cations, with the charge equalization decisively determining the number of these cations.
Such triaryl phosphines containing two phosphorus atoms of formula (II) and (III) comprise in particular four to eight xe2x80x94SO3M groups. The xe2x80x94SO3M are customarily located at the aryl groups of the group xe2x80x94(CH2)xxe2x80x94Arxe2x80x94Arxe2x80x94(CH2)xxe2x80x94 and at the two further aryl groups bound to the phosphorus.
Instead of sulfonated triaryl phosphines, other triaryl phosphines can alternatively be used as ligands, in which the SO3M group is substituted by other groups which bring about the water solubility of the triaryl phosphine, such as for example PO3M2 groups.
According to an especially preferred embodiment, the crown ether is selected from the group 12-crown-4, 15-crown-5, 18-crown-6 and hydroxy methyl 18-crown-6.
The olefin can be selected from aliphatic, cycloaliphatic and araliphatic olefins, in particular from aliphatic and cycloaliphatic xcex1-olefins.
The olefinic compound can comprise one or several carbon-carbon double bonds. The carbon-carbon double bond can be terminal or nonterminal. Preferred are olefinic compounds with terminal carbon-carbon double bonds. Examples of xcex1-olefinic compounds (with terminal carbon-carbon double bond) are 1-alkenes, alkylalkenoates, alkylene alkanoates, alkenyl alkyl ethers and alkenols. Without claiming completeness, as xcex1-olefinic compounds are cited propene, 1-butene, 1-pentene, 1-HEXENE, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene and 1-dodecene.
Especially preferred are olefins which contain maximally 10, preferably maximally 8 carbon atoms.
In view of the industrial use of this process, the olefin is in particular selected from the group propene, 1-butene, 1-pentene and 1-hexene.
In view of the process according to the invention it was found to be optimal that the aqueous phase comprises 20 to 500 ppm, preferably 30 to 150 ppm, in particular 40 to 100 ppm, of rhodium. The ratio of rhodium to ligand can herein be between 1:10 and 1:1000, preferably between 1:50 and 1:200.
The aqueous phase comprising the catalyst can be produced in a comparatively simple manner, by dissolving in water a water-soluble rhodium salt, the trisulfonated triaryl phosphines and the compound having the formula (I). Without claiming completeness, suitable rhodium salts are: rhodium(III) sulfate, rhodium(III) nitrate, rhodium(III) carboxylates such as rhodium(III) acetate, rhodium propionate, rhodium butyrate and rhodium-2-ethylhexanoate. The aqueous phase can be used directly in the hydroformylation or be previously subjected to a performulation of the catalyst under reaction conditions in order to use it subsequently in the performulated form.
The aqueous phase can preferably comprise 2xc3x9710xe2x88x926 to 5xc3x9710xe2x88x922 mol of rhodium per mol of olefinic compound.
During the reaction the pressure is in general between 20 and 150 bars, preferably between 30 and 80 bars. The ratio of carbon monoxide and hydrogen can vary within wide limits. Optimal is a ratio of carbon monoxide to hydrogen of 10:1 to 1:30, in particular of 5:1 to 1:8, preferably of 1:2 to 2:1. Especially preferred is the addition under pressure of synthesis gas at a ratio of carbon monoxide to hydrogen of 1:1.
During the reaction the temperature is customarily between 20 and 170xc2x0 C., preferably between 100 and 140xc2x0 C.
As the reaction vessels are used pressure reactors with magnetic or mechanical agitating or mixing devices. During the conversion a thorough mixing of the phases present, i.e. of polar phase, carbon monoxide/hydrogen and, if appropriate, organic phase must be ensured. This can be brought about in particular by intensive agitation and/or transferring by pumping of organic and aqueous phase. Continuous guidance of the experiment is also possible.
At the end of the reaction the pressure reactor is cooled, freed of carbon monoxide and hydrogen by pressure reduction and the reaction mixture is removed. After the mixing device is switched off, the phases separate by themselves within seconds. The organic phase can be processed by distillation and subsequently, if required, be analyzed by gas chromatography.
The following examples serve to explain the invention.